assume cs:code stack segment db 128 dup (0) stack ends code segment start: mov ax,stack mov ss,ax mov sp,128 push cs pop ds mov ax,0 mov es,ax mov si,offset int9 mov di,204h mov cx,offset int9end-offset int9 cld rep movsb push es:[9*4] pop es:[200h] push es:[9*4+2] pop es:[202h] cli mov word ptr es:[9*4],204h mov word ptr es:[9*4+2],0 sti mov ax,4c00h int 21h int9: push ax push bx push cx push es in al,60h pushf call dword ptr cs:[200h] cmp al,3bh jne int9ret mov ax,0b800h mov es,ax mov bx,1 mov cx,2000 s: inc byte ptr es:[bx] add bx,2 loop s int9ret:pop es pop cx pop bx pop ax iret int9end:nop code ends end start